Kanchan Ghosal

A high concentration photovoltaic module utilizing micro-transfer printing and surface mount technology

We describe a high concentration photovoltaic (CPV) module utilizing micro-transfer printed (µ-TP) dual-junction GaInP/GaAs solar cells and an ELO (Epitaxial Lift-Off) process used to fabricate very small cells (<0.5 mm2) using 1st use and reused GaAs substrates. The benefits of this technology include high efficiency, simple distributed heat transfer at high concentration ratios, and short optical paths. This approach enables the use of low cost, high reliability surface mount assembly of large backplanes for integration into CPV modules. To minimize compound semiconductor use and maximize cell efficiency, we combine plano-convex primary and spherical secondary optics to concentrate sunlight 1000X over a +/−0.8 degree angle of acceptance. Receiver efficiencies of ELO dual-junction GaInP/GaAs cells of >30% at 1,000 sun concentration are reported. Coupled with a >80% efficient optical train, module efficiencies greater than 24% have been achieved with dual-junction µ-TP solar cells.

A New Approach For A Low Cost CPV Module Design Utilizing Micro‐Transfer Printing Technology

Semprius is applying a novel massively parallel, automated production process to address CPV’s reliability, performance, cost, and scalability requirements. The new design approach utilizing patented micro‐transfer printing technology enables the use of many very small cells (0.36 mm2) with benefits including high efficiency, simple distributed heat transfer, high concentration ratio, and small thin concentrating optical elements. We briefly describe the design approach and provide detailed supporting on‐sun measurements.

HCPV Characterization: Analysis of Fielded System Data.

Sandia and Semprius have partnered to evaluate the operational performance of a 3.5 kW (nominal) R&D system using 40 Semprius modules. Eight months of operational data has been collected and evaluated. Analysis includes determination of Pmp, Imp and Vmp at CSTC conditions, Pmp as a function of DNI, effect of wind speed on module temperature and seasonal variations in performance. As expected, on-sun Pmp and Imp of the installed system were found to be ∼10% lower than the values determined from flash testing at CSTC, while Vmp was found to be nearly identical to the results of flash testing. The differences in the flash test and outdoor data are attributed to string mismatch, soiling, seasonal variation in solar spectrum, discrepancy in the cell temperature model, and uncertainty in the power and current reported by the inverter.. An apparent limitation to the degree of module cooling that can be expected from wind speed was observed. The system was observed to display seasonal variation in performance, li...

Performance of a micro-cell based transfer printed HCPV system in the South Eastern US

Printed micro-cells are the basis of a more cost effective and highly efficient HCPV module design. Module efficiencies of 33.9% at STC have been demonstrated for modules designed for commercial use. An array of these modules were deployed in a 3.5 kW system in Huntsville, AL to validate the design, demonstrate the reliability of the system and collect on-sun data to understand system performance. The first six months of performance data is presented along with results from soiling experiments.

Pressure activated interconnection of micro transfer printed components

Micro transfer printing and other forms of micro assembly deterministically produce heterogeneously integrated systems of miniaturized components on non-native substrates. Most micro assembled systems include electrical interconnections to the miniaturized components, typically accomplished by metal wires formed on the non-native substrate after the assembly operation. An alternative scheme establishing interconnections during the assembly operation is a cost-effective manufacturing method for producing heterogeneous microsystems, and facilitates the repair of integrated microsystems, such as displays, by ex post facto addition of components to correct defects after system-level tests. This letter describes pressure-concentrating conductor structures formed on silicon (1 0 0) wafers to establish connections to preexisting conductive traces on glass and plastic substrates during micro transfer printing with an elastomer stamp. The pressure concentrators penetrate a polymer layer to form the connection, and...

On‐Sun Performance of a Novel Microcell Based HCPV System Located in the Southwest US

Semprius has developed a novel microcell based, highly scalable HCPV module that addresses performance, cost and reliability requirements for utility scale solar installations. Semprius has fabricated dual junction cell based engineering prototype modules with 1000X concentration based on this technology. A 1 kW HCPV system using these modules was installed in Tucson to validate the technology and acquire on‐sun data. Eight months of on‐sun results from this system are presented.

Miniature Heterogeneous Fan-Out Packages for High-Performance, Large-Format Systems

High-throughput assembly of miniature wafer-fabricated packages onto panel substrates provides a manufacturing framework for high-performance multi-functional displays and other large-format systems. Control circuits, light emitters, sensors, and other micro-components formed in high-density arrays on wafers use a variety of processes and materials that do not easily translate to large-format panel processing. Systems assembled from some or all of those components can therefore exhibit combinations of properties and performance characteristics that are difficult to achieve by panel processes only. Here, we demonstrate hierarchical assembly strategies for fabricating high-performance systems using elastomer stamp micro-transfer-printing. In this work, red, green and blue microscale inorganic LEDs (µILEDs) are fabricated on their respective native wafer substrates and then assembled onto non-native intermediate silicon wafers. The intermediate silicon wafer, populated with heterogeneous µILEDs, then undergoes conventional wafer-level processes, such a dielectric depositions and thin-film metallization, to form miniature fan-out packages. Here, we will demonstrate three heterogeneous µILEDs integrated within a 75 µm × 35 µm fan-out package. We will present how this microscale package can be undercut and then micro-transfer-printed directly onto large-format application substrates. The print-compatible packages also include sharp pressure-concentrating conductor structures which allow the heterogeneous fan-out packages to be electrically interconnected to large-format substrates during the printing operation. We will present functional µILED displays that have been fabricated using these assembly techniques. We will report on the benefits of using intermediate packaging substrates for manufacturing of high-performance large-format systems, such as displays. We will also demonstrate strategies for repairing large multi-functional systems.

Pressure-Activated Electrical Interconnection During Micro-Transfer-Printing

Sharp electrically conductive structures integrated into micro-transfer-print compatible components provide an approach to forming electrically interconnected systems during the assembly procedure. Silicon micromachining techniques are used to fabricate print-compatible components with integrated, electrically conductive, pressure-concentrating structures. The geometry of the structures allow them to penetrate a polymer receiving layer during the elastomer stamp printing operation, and reflow of the polymer following the transfer completes the electrical interconnection when capillary action forces the gold-coated pressure-concentrator into a metal landing site. Experimental results and finite element simulations support a discussion of the mechanics of the interconnection.

Ultrahigh Efficiency HCPV Modules and Systems

Semprius manufactures high-concentration photovoltaic (HCPV) modules and systems. Module characterization and quality control methods are described in this paper. Module efficiency distribution for thousands of modules is presented, currently showing an increase in average efficiency from 33% in 2013 to 35%. Data from modules and systems in the field are presented showing consistent performance over all seasons and no apparent degradation after 3 years. Finally, the effect of ambient temperature and wind speed on performance was studied.

Semprius field results

Semprius has increased its printed micro-cell module efficiency to 35.5% at CSTC. This design has been field tested for more than two years with no measurable signs of degradation. Three different commercial ready CPV systems have been designed, installed and characterized. The pointing error of all three trackers is ±0.1°, well within the module angle of acceptance (AOA) of ±0.8°. The on-sun performance of these systems is consistent with expectations. The peak AC efficiency of the systems was ∼30%.